In part, van Dijk said, the practice has been beneficial. He recently surveyed four major Chinese turtle markets and found that the large majority of turtles came from farms.

"Wild-collected turtles—nearly all tropical Asian species—have reduced from 70 percent market share in 2000 to about 30 percent market share now in the visible trade in South China," he said.

Other factors may also have contributed to the change, such as improved import restrictions as well as the sobering fact that many Southeast Asian turtle populations are greatly depleted.

But at the same time, commercial breeding has placed significant new pressures on Chinese species, nearly all of which are threatened.

"Farming is a major additional impact on Chinese wild turtle populations but probably the savior for Southeast and South Asian turtles," van Dijk said.

In China, he said, turtle farming "has the potential to place a premium value on the very last wild animals, which means it will be profitable and economically worthwhile for local collectors to go out and look for them."

Letter co-author Parham agreed, adding that "the demand for [breeding stock] is real. For some species, such as the coveted golden coin turtle, the desire for wild-caught males can be extremely high."

International Turtle Soup

As Chinese turtles become increasingly rare, Parham said, farmers have been turning to non-native species. Sliders and snapping turtles from the United States are a growing part of Asia's farming trade.

Commercial-scale harvest of wild turtles in the U.S. for export to China is a growing phenomenon, subject to only minimal regulations in many areas, he noted.

"Some of these turtles inevitably escape into the wild, potentially spreading disease or competing with native Chinese species," Parham said.

Impacts are also expected at the other end of the supply chain.

The nonprofit World Chelonian Trust documented exports of more than 700,000 wild-caught U.S. turtles from 2003 to 2005. The majority went to Asian turtle farms and food markets.

China's appetite for turtle soup has already reduced populations of Maryland's state reptile, the diamondback terrapin. The state legislature is now considering bills that would permanently ban commercial terrapin harvests.

"This is definitely a growing trend, and we are very concerned about it," van Dijk said.

Parham also points to a more recent example from Texas. As reported in several newspapers, a local businessman has been recruiting assistants to help capture 300,000 wild turtles a year for export to Asia.

Common snapping turtles and red-eared sliders—both relatively abundant species—are the primary targets. But biologists worry that threatened species such as the alligator snapping turtle may inadvertently be affected.